Erotic spanking (also known as spankophilia) is the act of spanking another person for the sexual arousal or gratification of either or both parties. Activities range from a spontaneous smack on bare buttocks during a sexual activity, to occasional sexual roleplay (such as ageplay) to domestic discipline and may involve the use of a hand or the use of a variety of spanking implements, such as a spanking paddle or cane. Erotic spanking may be administered to bare buttocks or normally dressed. Spanking can involve the use of bondage.
Erotic spankings are commonly combined with other forms of sexual foreplay, such as oral sex, sexual roleplaying and/or ageplay. The most common type of erotic spanking is administered on the bare buttocks, but can also be combined with bondage, in order to heighten sexual arousal and feelings of helplessness.
Many cultures describe pain as an aphrodisiac. For example, the Kama Sutra, in particular, goes into specific detail on how to properly strike a partner during sex. (WIKIPEDIA)